This invention relates to an electrostatographic printing machine, and more particularly to an apparatus for developing a latent image recorded on an imaging surface with a liquid developer.
A typical electrostatographic printing machine employs a photoconductive member that is sensitized by charging to a substantially uniform potential. The charged portion of the photoconductive member is exposed to the light image of a document. Exposure of the charged photoconductive member selectively dissipates the charge to record an electrostatic latent image. The electrostatic latent image corresponds to the informational areas of the document. The electrostatic latent image recorded on the photoconductive member is developed by contact with a developer material. The developer material can be a dry material comprising carrier granules having adhering toner particles. The latent image attracts the toner particles from the carrier granules to form a toner powder image on the photoconductive surface. The toner powder image is then transferred and permanently fused to a copy sheet.
An electrostatic latent image also may be developed with a liquid developer material. In a liquid development system, the photoconductive surface is contacted with an insulating liquid carrier having dispersed finely divided marking particles. The electrical field associated with the electrostatic latent image attracts the marking particles to the photoconductive surface to form a visible image.
Liquid developing imaging processes utilize a liquid developer typically having about 2 percent by weight of fine solid particulate toner material dispersed in a liquid carrier. The liquid carrier is typically a hydrocarbon. In the developing process, the image is transferred to a receiver which may be an intermediate belt. The image on the photoreceptor contains about 12 weight percent of particulate toner in liquid hydrocarbon carrier. To improve the quality of transfer of developed image to receiver, percent solids in liquid should be increased to about 25 percent by weight. Increase in percent solids may be achieved by removing excess hydrocarbon liquid. However, excess hydrocarbon liquid must be removed in a manner that results in minimum degradation of the toner image.
U.S. Pat. No. 3,866,572, to Gundlach, Feb. 18, 1975, relates to an electrostatographic apparatus wherein a transfer bias voltage is applied between a roller electrode and a first support surface to provide an electrical field for transfer between roller and surface. The roller electrode comprises an electrically conductive core. The bias voltage is applied to the core spaced from the first support surface. A thick highly compressible roller body of foraminous open cell material extends between the conductive core and the first support surface. The foraminous material has a multiplicity of small discontinuities providing an ionization control barrier. The foraminous material may be compressed between the conductive core and the first support surface to a thickness approximately one-half of its normal uncompressed thickness.
U.S. Pat. No. 4,089,683, to Knieser, May 16, 1978, relates to an apparatus for eliminating transfer of residual liquid developer from an imaging surface. The imaging surface is contacted with an advancing, transversely-oriented foam belt. The belt has a pattern of raised and depressed areas to redistribute streaks and deposits of liquid developer remaining on the imaging surface.
U.S. Pat. No. 4,258,115, to Magome et al., Mar. 24, 1981, discloses a device for wet developing an electrostatic image comprising a bearing member for forming a pool of developing liquid and a developing member for supplying developing liquid and collecting excess liquid. The developing member is an elastic member formed into a roller.
U.S. Pat. No. 4,263,391, to Saito et al., Apr. 21, 1981, discloses an elastic rotary member with an electroconductive core member, an electroconductive porous elastic member capable of retaining a liquid and provided around the core member and a liquid-permeable insulating member surrounding the outer periphery of the elastic member. The elastic rotary member is maintained in pressure contact with the latent image carrying member whereby liquid developer is squeezed out from the elastic rotary member and excessive liquid developer present on the latent image carrying member is recovered by absorption upon recovery of the elastic rotary member from a compressed state.
U.S. Pat. No. 4,707,112, to Hartmann, Nov. 17, 1987, relates to an apparatus for developing an electrostatic latent image. The apparatus includes means for furnishing liquid developer material to the image in a development zone and means for dispersing the particles substantially uniformly in the liquid carrier of the liquid developer material at the entrance to the development zone so as to deflocculate marking particles. The dispersing means may comprise means for generating a pulsed electrical field in the developer material at the entrance to the development zone to induce movement of the marking particles and the liquid carrier. The generating means includes an electrode positioned at the entrance to the development zone and means for applying a pulsed voltage to the electrode to generate a pulsed electrical field in the developer material.
The present invention provides an improved apparatus for application of carrier liquid to a photoreceptor and an improved electrostatographic imaging process.